Forging-rolling combined preparation method of high-strength and high-toughness titanium alloy small-specification bar for machining

Abstract

The invention relates to a forging-rolling combined preparation method of a high-strength and high-toughness titanium alloy small-specification bar for machining, which comprises three stages of a cogging forging step, a two-phase region forging step, and a drawing blank making and rolling forming post-heat treatment step. As-cast grains can be fully crushed; a rolling forming mode is utilized, the heating number can be effectively reduced, and the production efficiency and the batch stability are improved; and the prepared small-specification bar with the diameter being 40-80 mm can be directly machined to form a part subsequently, die forging is not needed, the production cost of the small part can be effectively reduced, and important economic and military values are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of titanium alloy material processing, in particular to a forging-rolling combined preparation method for a titanium alloy bar. Background Art

[0002] In the field of aerospace engineering, the importance of titanium alloy as the core structural material of aircraft and engines is self-evident. In view of the increasingly stringent requirements of new aviation structural parts for material properties and process performance, the design and development of titanium alloys are moving towards the comprehensive optimization of high strength and high toughness. At present, in the traditional field, high-strength and high-toughness titanium alloys represented by near-β-type titanium alloys Ti-1023 and BT22 (i.e. domestic TC18, with a nominal chemical composition of Ti-5Al-5Mo-5V-1Fe-1Cr) occupy an important position.

[0003] However, with the rapid development of aerospace technology, the exploration and research and development of new titanium alloys are also continuing to deepen. Among them, Ti55531 titanium alloy, as a high-strength and tough metastable β-type titanium alloy optimized based on BT-22 in cooperation with VSMPO and Airbus, has demonstrated its unique advantages. Ti55531 (nominal composition is Ti-5Al-5V-5Mo-3Cr-1Zr) is rich in β-phase stabilizing elements such as molybdenum, vanadium, chromium, etc. The high content of these elements not only ensures the stable retention of the β phase of the alloy during quenching, but also enables it to have a lower α / β phase transition temperature range (approximately 820-860°C), providing a wider adjustment space for the heat treatment process of the material. The Mo equivalent of this alloy is greater than 13, and after heat treatment, its tensile strength can reach more than 1400MPa, which is a typical high-strength titanium alloy.

[0004] Compared with traditional alloys such as Ti-1023, Ti55531 has many advantages in performance, including but not limited to lower smelting and processing costs, significant resistance to component segregation, excellent specific strength and tensile strength, excellent fracture toughness, good hardenability up to 250mm or more, and high adaptability to different processing conditions. These characteristics together give Ti55531 alloy the ability to achieve fine control between strength and toughness, thereby demonstrating its extraordinary comprehensive mechanical properties. In view of its excellent performance, Ti55531 titanium alloy is highly favored in the aviation field and has been widely used in the manufacture of key load-bearing components of large transport aircraft such as Airbus A380 and other super-large long-range wide-body aircraft, especially in high-strength and high-stress areas such as wing and pylon connection devices. The application of Ti55531 alloy further demonstrates its core value in the modern aviation industry.

[0005] So far, the high-strength and high-toughness Ti55531 titanium alloy has not been used in large-scale industrial applications in China. Compared with foreign countries, there is still a certain gap in the maturity of Ti55531 titanium alloy smelting and forging technology and quality control. Therefore, there is an urgent need for a method that can realize the preparation process of this titanium alloy and its quality control. Summary of the invention

[0006] The purpose of the present invention is to avoid the shortcomings of the prior art and provide a forging-rolling combined preparation method for machining small-sized titanium alloy bars with high strength and high toughness of Φ40-70 mm, which can be directly machined into parts without die forging, thereby effectively reducing the production cost of parts.

[0007] To achieve the above object, the technical solution adopted by the present invention is: a forging-rolling combined preparation method of small-sized high-strength and high-toughness titanium alloy bars for machining, comprising the following steps:

[0008] Step 1, subjecting the titanium alloy ingot to three-stage open forging with a deformation amount of 30-50% and a deformation rate of 10-30 mm / s at a temperature condition of 100°C-350°C above the β transformation temperature, 30°C-60°C below the β transformation temperature, and 30°C-50°C above the β transformation temperature, and performing open forging for at least 1-2 times in each stage, so as to obtain a titanium alloy billet;

[0009] Among them, after each stage of billet forging, the billet is air-cooled to room temperature before the next stage of billet forging is carried out;

[0010] Step 2, under the heating temperature condition of 30°C to 60°C below the β transformation temperature, the titanium alloy billet is subjected to upsetting forging with a deformation amount of 30 to 50% and a deformation rate of 10 to 30 mm / s, and at least 2 times of upsetting forging are performed, and air cooling is performed to room temperature after upsetting forging;

[0011] Step 3, for the titanium alloy billet after the billet forging, sequentially perform billet drawing at a heating temperature of 30°C to 60°C below the β transformation temperature, with a deformation amount of 20 to 50%, and a deformation rate of 10 to 30 mm / s, and rolling at a heating temperature of 10°C to 40°C below the β transformation temperature, with a deformation amount of 15 to 40%, and a deformation rate of 10 to 30 mm / s, and finally perform β annealing and aging heat treatment and then air cool to room temperature to obtain a titanium alloy bar with a diameter of 40 to 80 mm;

[0012] Among them, after drawing forging and rolling, they are air-cooled to room temperature.

[0013] Furthermore, in step 1:

[0014] The heating process of the first stage of blank forging is to first heat the cold material of the titanium alloy ingot to 700-900°C, keep it warm for 100-140 minutes, then heat it to a temperature of 100-350°C above the β transformation temperature, keep it warm, and the insulation coefficient is 0.6-0.8, and then carry out blank forging after being taken out of the furnace;

[0015] At the same time, during the first stage of blank forging, the sawn surface of the titanium alloy ingot is riveted and upset. The riveted and upset method is to first upset half of it, turn it over, and then upset it to size.

[0016] Furthermore, in step 1:

[0017] In the first stage of billet forging, 2 to 4 times of upsetting forging are performed, the deformation amount of each time is 30 to 50%, the deformation rate is 10 to 30 mm / s, 1 to 2 times of upsetting forging are performed during the upsetting forging, and the deformation rate is not more than 30 mm / s, and the reduction amount of a single time is not more than 150 mm;

[0018] In the second stage of blank forging, 1 to 2 times of upsetting and drawing forging are performed, with the deformation amount of each time being 30 to 50% and the deformation rate being 10 to 30 mm / s;

[0019] In the third stage of blank forging, 1 to 2 rounds of upsetting forging are performed, with the deformation amount of each round being 30 to 50% and the deformation rate being 10 to 30 mm / s.

[0020] Furthermore, in the step 2, the titanium alloy billet is subjected to 1 to 3 rounds of upsetting and drawing forging, with a deformation amount of 30 to 50% in each round and a deformation rate of 10 to 30 mm / s, and 1 to 2 rounds of diagonal drawing are performed during the period, with a drawing speed of no more than 30 mm / s and a reduction amount of no more than 200 mm in a single round.

[0021] Furthermore, the thermal insulation coefficient of the heating process in step 1 and step 2 is 0.6 to 0.8.

[0022] Furthermore, the drawing and blanking in step three is specifically: the titanium alloy billet after upsetting and forging is subjected to 4 to 6 drawing deformations, the deformation amount of each fire is 20 to 50%, the deformation rate is 10 to 30 mm / s, and the thermal insulation coefficient of the heating process is 0.6 to 0.8.

[0023] Furthermore, the rolling in step three is specifically to perform 1 to 2 rolling deformations on the drawn titanium alloy material, with the deformation amount of each rolling being 15 to 40%, the deformation rate being 10 to 30 mm / s, and the thermal insulation coefficient of the heating process being 0.6 to 0.8.

[0024] Furthermore, the beta annealing and aging heat treatment in step three are specifically:

[0025] Under the condition that the annealing heating temperature is 10℃~40℃ above the β transformation temperature and the temperature is kept for 1~2h, β annealing is carried out, then, after furnace cooling to the aging temperature of 510~560℃, it is kept for 8~10h and air cooling is completed, wherein the cooling rate in the furnace cooling stage is 1~3℃ / min.

[0026] Furthermore, the heating and forging processes in the drawing and billet making in step 2 and step 3 are respectively carried out in a heating furnace and a fast forging machine, the transfer time of the titanium alloy billet from the heating furnace to the fast forging machine is not more than 50S, and the final forging temperature is not less than 650°C.

[0027] Furthermore, the titanium alloy is Ti55531 or tc18 or TB6 titanium alloy.

[0028] The beneficial effects of the present invention are as follows: the present invention provides a forging-rolling combined preparation method for small-sized titanium alloy bars for machining. Compared with conventional forged bars, the forging pressure advantage of a 100MN large-tonnage fast forging machine is utilized to provide a large deformation amount during the ingot blanking deformation, which can fully crush the cast grains; the rolling forming method is utilized to effectively reduce the number of fires, improve production efficiency and batch stability; the prepared Φ40-80mm small-sized bars can be subsequently directly machined into parts without die forging, which can effectively reduce the production cost of small parts and has important economic and military value. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a flow chart of the method of the present invention;

[0030] Figure 2 The microstructure of the Φ160 mm rod before rolling of Ti55531 titanium alloy in the specific example of the present invention;

[0031] Figure 3 This is the finished product morphology of the small-sized Ti55531 titanium alloy bar in the specific example of the present invention;

[0032] Figure 4 This is the heat-treated microstructure of a small-sized Ti55531 titanium alloy bar in a specific example of the present invention. DETAILED DESCRIPTION

[0033] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0034] In order to achieve the above object, the present invention provides the following specific implementation methods:

[0035] Example 1: A forging-rolling combined preparation method for small-sized high-strength and high-toughness titanium alloy bars for machining, using Ti55531 or tc18 or TB6 titanium alloy, and the method includes the following steps:.

[0036] Step 1, subjecting the titanium alloy ingot to three-stage open forging with a deformation amount of 30-50% and a deformation rate of 10-30 mm / s at a temperature condition of 100-350°C above the β transformation temperature, 30-60°C below the β transformation temperature, and 30-50°C above the β transformation temperature, and performing open forging for at least 1-2 times in each stage, and a heat preservation coefficient of 0.6-0.8 during the heating process, so as to obtain a titanium alloy billet; wherein, after each stage of open forging, air cooling is performed to room temperature before the next stage of open forging is performed;

[0037] Step 2, under the heating temperature condition of 30°C to 60°C below the β transformation temperature, the titanium alloy billet is subjected to upsetting forging with a deformation amount of 30 to 50% and a deformation rate of 10 to 30 mm / s, and at least 2 times of upsetting forging are performed, and air cooling is performed to room temperature after upsetting forging;

[0038] Among them, the heating and forging processes in the step 2 are carried out in a heating furnace and a fast forging machine respectively, the transfer time of the titanium alloy billet from the heating furnace to the fast forging machine is not more than 50S, the final forging temperature is not less than 650°C, the insulation coefficient of the heating process is 0.6-0.8, and the whole process is carried out in a heating furnace and a fast forging machine respectively, the transfer time of the titanium alloy billet from the heating furnace to the fast forging machine is not more than 50S, and the final forging temperature is not less than 650°C.

[0039] Step 3, for the titanium alloy billet after the billet forging, sequentially perform billet drawing at a heating temperature of 30°C to 60°C below the β transformation temperature, with a deformation amount of 20 to 50%, and a deformation rate of 10 to 30 mm / s, and rolling at a heating temperature of 10°C to 40°C below the β transformation temperature, with a deformation amount of 15 to 40%, and a deformation rate of 10 to 30 mm / s, and finally perform β annealing and aging heat treatment and then air cool to room temperature to obtain a titanium alloy bar with a diameter of 40 to 80 mm;

[0040] Specifically, the drawing process is as follows: the titanium alloy billet after upsetting and drawing is subjected to 4 to 6 drawing deformations, the deformation amount of each drawing is 20 to 50%, the deformation rate is 10 to 30 mm / s, and the insulation coefficient of the heating process is 0.6 to 0.8; the heating and forging processes in the drawing process are respectively carried out in a heating furnace and a fast forging machine, the transfer time of the titanium alloy billet from the heating furnace to the fast forging machine is not more than 50S, and the final forging temperature is not less than 650°C.

[0041] Specifically, the drawn titanium alloy is subjected to 1-2 rolling deformations, the deformation amount of each rolling is 15-40%, the deformation rate is 10-30 mm / s, and the heat preservation coefficient of the heating process is 0.6-0.8.

[0042] After drawing, forging and rolling, the steel is air-cooled to room temperature.

[0043] At the same time, the beta annealing and aging heat treatment are specifically:

[0044] Under the condition that the annealing heating temperature is 10℃~40℃ above the β transformation temperature and the temperature is kept for 1~2h, β annealing is carried out, then, after furnace cooling to the aging temperature of 510~560℃, the temperature is kept for 8~10h, and the aging heat treatment is completed by air cooling, wherein the cooling rate in the furnace cooling stage is 1~3℃ / min.

[0045] Embodiment 2: The same as Embodiment 1, except that: the heating process of the first stage of blank forging is to first heat the cold material of the titanium alloy ingot to 700-900°C, and keep it warm for 100-140 minutes, and then heat it to a temperature condition of 100-350°C above the β transformation temperature, and keep it warm, and the insulation coefficient is 0.6-0.8, and blank forging is carried out after being kept warm.

[0046] At the same time, during the first stage of billet forging, the sawn surface of the titanium alloy ingot is riveted and upset. The riveted and upset method is to first upset half of it, turn it over, and then upset it to size.

[0047] In the first stage of blank forging, 2 to 4 times of upsetting forging are performed, the deformation amount of each time is 30 to 50%, the deformation rate is 10 to 30 mm / s, 1 to 2 times of upsetting forging are performed during the upsetting forging, and the deformation rate is not more than 30 mm / s, and the reduction amount of a single time is not more than 150 mm;

[0048] In the second stage of blank forging, 1 to 2 times of upsetting and drawing forging are performed, with the deformation amount of each time being 30 to 50% and the deformation rate being 10 to 30 mm / s;

[0049] In the third stage of blank forging, 1 to 2 rounds of upsetting forging are performed, with the deformation amount of each round being 30 to 50% and the deformation rate being 10 to 30 mm / s.

[0050] Example 3: The same as Example 1, except that in step 2, the titanium alloy billet is subjected to 1 to 3 rounds of upsetting and drawing forging, the deformation amount of each round is 30 to 50%, the deformation rate is 10 to 30 mm / s, and 1 to 2 rounds of diagonal drawing are performed during the period, the drawing speed is not more than 30 mm / s, and the reduction amount in a single round is not more than 200 mm.

[0051] In order to further describe the technical scheme and technical effects of the present invention, the present invention provides the following specific examples:

[0052] Specific examples: Figure 1-Figure 4 As shown, a forging-rolling preparation method for a small-sized high-strength and high-toughness Ti55531 titanium alloy bar for machining includes the following steps:

[0053] Step 1, "high-low-high" blank forging: the Ti55531 titanium alloy ingot is subjected to three-stage upsetting and drawing forging at 350°C, 250°C and 150°C above the β transformation temperature, respectively, with a deformation of about 40%. During the second stage, a reversing drawing is performed, wherein the deformation rate in the upsetting and drawing forging is not more than 30 mm / s, and the single pressing amount is not more than 150 mm; air cooling is adopted after forging;

[0054] Then the second stage 1 fire upsetting forging is carried out at 60℃ below the β transformation temperature, with a deformation of about 35%;

[0055] Finally, the third stage 1 fire upsetting forging is carried out at 50℃ above the β transformation temperature, with a deformation of about 40%, and air cooling is used after forging;

[0056] Among them, when heating the cold material for forging above the β transformation temperature, the alloy is first heated to 800℃ and kept warm for 120min, and then heated to the required temperature for insulation, and the insulation coefficient is 0.7; during the first upsetting, the sawn surface of the ingot needs to be riveted and upset, and the upsetting method is adopted to upset half first, turn over and then upset to size.

[0057] Step 2, two-phase low-temperature forging: Under the heating temperature condition of 45-60°C below the β transformation temperature, the billet treated in step 1 is subjected to one upsetting forging, the deformation amount of upsetting forging is about 35%, during which one diagonal stretching is performed, the deformation rate is not more than 30mm / s, the single pressing amount is not more than 200mm, the insulation coefficient of the heating process is 0.7, and air cooling is adopted after upsetting forging; the transfer time of the billet from the heating furnace to the fast forging machine is not more than 50S, and the final forging temperature is not less than 650°C.

[0058] Step 3, drawing and forging: the billet processed in step 2 is drawn and forged to a specified size of the rolled billet, and the heating temperature is 60°C below the β transformation temperature, and air cooling is adopted after the drawing and forging;

[0059] Among them, the drawing forging is to draw the billet for 5 times, the deformation is controlled between 20% and 50%, the deformation rate is 10-30mm / s, and the insulation coefficient of the heating process is 0.7. The transfer time of the billet from the heating furnace to the fast forging machine is no more than 50S, and the final forging temperature is no less than 650℃.

[0060] Step 4, rolling forming: under the conditions of heating temperatures of 10-20°C and 25-35°C below the β transformation temperature, the billet treated in step 3 is rolled twice, with deformation amounts of 38%-40% and deformation rates of 10-30 mm / s, respectively. The insulation coefficient of the heating process is 0.7, and air cooling is adopted after rolling; the transfer time of the billet from the heating furnace to the fast forging machine is not more than 50S, and the final forging temperature is not less than 650°C.

[0061] Step 5, bar heat treatment: the bar treated in step 4 is subjected to β annealing + aging heat treatment, and the β annealing heating temperature is 20°C above the β transformation temperature, kept warm for 2h, furnace cooled to the aging temperature and kept warm for 8h, the aging temperature is 530°C, the furnace cooling speed is controlled at 1.5°C / min, and the aging heat treatment is completed by air cooling.

[0062] Through the above five steps, Ti55531 titanium alloy rods with a diameter of 40 to 80 mm are obtained.

[0063] Experimental results:

[0064] like Figure 2 and Figure 3 As shown, the Φ50mm Ti55531 titanium alloy small-size bar produced by the forging-rolling combined preparation method of the present invention for machining high-strength and high-toughness Ti55531 titanium alloy small-size bar has a normal macrostructure and no metallurgical defects; Figure 4 As shown, the microstructure is uniform and is a lamellar structure; as shown in Table 1, Table 1 is a table of room temperature mechanical properties of Ti55531 titanium alloy Φ50mm small-size bars obtained in this specific example in the β annealing + aging state,

[0065] Table 1

[0066]

[0067] It can be seen from the table that the rods produced by this method have good matching of strength and toughness, can meet relevant standards and batch production requirements, and have important economic and military strategic significance.

[0068] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing small-sized high-strength and high-toughness titanium alloy bars for machining by forging-rolling combination, characterized in that: The following steps are involved: Step 1, subjecting the titanium alloy ingot to three-stage open forging with a deformation amount of 30-50% and a deformation rate of 10-30 mm / s at a temperature condition of 100°C-350°C above the β transformation temperature, 30°C-60°C below the β transformation temperature, and 30°C-50°C above the β transformation temperature, and performing open forging for at least 1-2 times in each stage, so as to obtain a titanium alloy billet; Among them, after each stage of billet forging, the billet is air-cooled to room temperature before the next stage of billet forging is carried out; Step 2, under the heating temperature condition of 30°C to 60°C below the β transformation temperature, the titanium alloy billet is subjected to upsetting forging with a deformation amount of 30 to 50% and a deformation rate of 10 to 30 mm / s, and at least 2 times of upsetting forging are performed, and air cooling is performed to room temperature after upsetting forging; Step 3, for the titanium alloy billet after the billet forging, sequentially perform billet drawing at a heating temperature of 30°C to 60°C below the β transformation temperature, with a deformation amount of 20 to 50%, and a deformation rate of 10 to 30 mm / s, and rolling at a heating temperature of 10°C to 40°C below the β transformation temperature, with a deformation amount of 15 to 40%, and a deformation rate of 10 to 30 mm / s, and finally perform β annealing and aging heat treatment and then air cool to room temperature to obtain a titanium alloy bar with a diameter of 40 to 80 mm; Among them, after drawing forging and rolling, they are air-cooled to room temperature.

2. The forging-rolling combined preparation method of small-sized high-strength and high-toughness titanium alloy bars for machining as claimed in claim 1 is characterized in that: In the step 1: The heating process of the first stage of blank forging is to first heat the cold material of the titanium alloy ingot to 700-900°C, keep it warm for 100-140 minutes, then heat it to a temperature of 100-350°C above the β transformation temperature, keep it warm, and the insulation coefficient is 0.6-0.8, and then carry out blank forging after being taken out of the furnace; At the same time, during the first stage of blank forging, the sawn surface of the titanium alloy ingot is riveted and upset. The riveted and upset method is to first upset half of it, turn it over, and then upset it to size.

3. The forging-rolling combined preparation method of small-sized high-strength and high-toughness titanium alloy bars for machining as claimed in claim 1, characterized in that: In the step 1: In the first stage of billet forging, 2 to 4 times of upsetting forging are performed, the deformation amount of each time is 30 to 50%, the deformation rate is 10 to 30 mm / s, 1 to 2 times of upsetting forging are performed during the upsetting forging, and the deformation rate is not more than 30 mm / s, and the reduction amount of a single time is not more than 150 mm; In the second stage of blank forging, 1 to 2 times of upsetting and drawing forging are performed, with the deformation amount of each time being 30 to 50% and the deformation rate being 10 to 30 mm / s; In the third stage of blank forging, 1 to 2 rounds of upsetting forging are performed, with the deformation amount of each round being 30 to 50% and the deformation rate being 10 to 30 mm / s.

4. The forging-rolling combined preparation method of small-sized high-strength and high-toughness titanium alloy bars for machining as claimed in claim 1, characterized in that: In the step 2, the titanium alloy billet is subjected to 1 to 3 rounds of upsetting and drawing forging, with the deformation amount of each round being 30 to 50% and the deformation rate being 10 to 30 mm / s, and 1 to 2 rounds of diagonal drawing are performed during the process, with the drawing speed being no more than 30 mm / s and the reduction amount of a single round being no more than 200 mm.

5. The forging-rolling combined preparation method of small-sized high-strength and high-toughness titanium alloy bars for machining as claimed in claim 1, characterized in that: The thermal insulation coefficient of the heating process in step 1 and step 2 is 0.6 to 0.

8.

6. The forging-rolling combined preparation method for small-sized high-strength and high-toughness titanium alloy bars for machining as claimed in claim 1, characterized in that: The drawing and blanking in step three specifically comprises: subjecting the titanium alloy blank after upsetting and drawing to drawing deformation for 4 to 6 times, with a deformation amount of 20 to 50% per time, a deformation rate of 10 to 30 mm / s, and a thermal insulation coefficient of 0.6 to 0.8 during the heating process.

7. The method for preparing small-sized high-strength and high-toughness titanium alloy bars for machining by forging-rolling combination according to claim 1, characterized in that: The rolling in step three is specifically to perform 1 to 2 rolling deformations on the drawn titanium alloy material, with the deformation amount of each rolling being 15 to 40%, the deformation rate being 10 to 30 mm / s, and the thermal insulation coefficient of the heating process being 0.6 to 0.

8.

8. The method for preparing small-sized high-strength and high-toughness titanium alloy bars for machining by forging-rolling combination according to claim 1, characterized in that: The beta annealing and aging heat treatment in step 3 are specifically: Under the condition that the annealing heating temperature is 10℃~40℃ above the β transformation temperature and the temperature is kept for 1~2h, β annealing is carried out, then, after furnace cooling to the aging temperature of 510~560℃, it is kept for 8~10h and air cooling is completed, wherein the cooling rate in the furnace cooling stage is 1~3℃ / min.

9. The method for preparing small-sized high-strength and high-toughness titanium alloy bars for machining by forging-rolling combination according to claim 1, characterized in that: The heating and forging processes in the step 2 and step 3 of drawing and billet making are respectively carried out in a heating furnace and a fast forging machine. The transfer time of the titanium alloy billet from the heating furnace to the fast forging machine is not more than 50S, and the final forging temperature is not less than 650°C.

10. The method for preparing small-sized high-strength and high-toughness titanium alloy bars for machining by forging-rolling combination according to any one of claims 1 to 9, characterized in that: The titanium alloy is Ti55531 or tc18 or TB6 titanium alloy.

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